Basically, the only places where it intersects with the Arles Way are some villages and towns near Toulouse, so that on the Arles Way the only "quick" diversion would be as a variant partial approach into the city.
Pretty much, the canal du midi goes nowhere near the Arles Way.
Having said that, there is a variant Way starting out from Montpellier to Béziers, then up from there towards Toulouse and the Arles Way ; so you could follow that to Béziers, then get onto the canal from there onwards, as the German pilgrim I met in Béziers was doing pretty much exactly.
Actually, for the first few K out of Béziers, the French Catalan Way basically goes along that canal.
There are a couple of albergues between Montpellier and Béziers, not very many, one in Gigean (15€), there's one at Saint-Thibéry (donativo AFAIK didn't stay there), and the donativo in Béziers itself is excellent.
The route is poorly waymarked, and it's mostly considered as a variant of the Piémont Way -- though actually it's four Ways in one. The oldest being the Cami Romieu from Catalonia towards Rome, it's older than the pilgrimage to Compostela itself ; part of the Piémont Way ; a variant of the Arles Way but going via Carcassonne, Castelnaudary ; and a route towards the French Catalan Way.